The present invention relates generally to tension regulating devices for use in conjunction with tensioning members such as chains, ropes and the like, and, more specifically, to a tension modifier used in combination with a tension regulating device.
In many applications where a tension member such as rope or cable is used, for example, to transmit a tension force or to restrain cargo during transport, it is desirable to minimize the effect of a sudden increase or decrease of tension in the tension member. Where the tension member is operatively attached to an article or container; such as when the tension member is used in lifting or towing applications, a sudden change in the tension applied to the tension member may result in injury to the secured article or container or their contents.
Another shortcoming of tension members becomes apparent when the tension member is adapted to restrict or contain a force directed against the tension member. For example, in the shipping industry, cargo is commonly tied down or otherwise restrained during transport by the use of inelastic restraining means such as chain or cable. The usefulness of the tension member in this situation depends on its ability to develop and maintain a force in opposition to the force applied by the restrained cargo. However, a slight decrease in the applied force often renders an inelastic tension member ineffective. Moreover, owing to the inelasticity of these restraining means and, as in the case of chain, the discrete nature of the adjustability, it is very difficult to initially secure the restraining means under satisfactory tension. Too, during transport, the cargo itself may settle or shift, thereby causing the restraining means to loosen or shift further. All of these situations may result in damage to or loss of the cargo. Even when the restraining means is adequately tensioned and positioned to restrain the cargo, it has no shock absorption properties to protect the cargo during transport.
Where the tension member is somewhat extensible, such as with rope or web strapping, some of the abovedescribed problems are alleviated inasmuch as an extensible restraining member may be initially adjusted to an adequate tension more easily. Used as a restraining means, an extensible tension member may also be pretensioned to compensate for a subsequent shift in the restrained cargo. However, the tension member by itself, even if extensible, offers minimal shock protection, and under a continuous load it may inelastically stretch and become loose, with the result that cargo may be damaged during transport because of inadequate restraint.
Conventional tension regulating devices that were designed to address the problems inherent in the use of tension members have generally been of a series spring construction or variations thereof. That is, a spring or other elastic member is inserted in line with a tension member to regulate the effect of a sudden change in the applied tension or, where the elastic member is pretensioned in restraining applications, to compensate for a shift or lengthening of the tension member by maintaining a somewhat uniform tension therein. This type of regulating device has several disadvantages, however. Owing to the series arrangement of the elastic member, tension regulation is accomplished by a change in the length of the regulating device as the elastic member stretches or contracts to counter a change in the applied tension. In many application, it is undesirable that the combined length of the tension member and the regulating device vary significantly.
Further, if the applied tension is too great, the regulating device may be stretched to a point where it deforms and loses its elasticity. To prevent this latter occurrence, some conventional tension regulating devices include a section of inextensible material secured across the elastic portion. The length of the inextensible section is such that at applied tensions which would deform the elastic portion, the inextensible section is pulled taut and bears most of the applied tension. Since the inextensible section has no tension regulating characteristics, the entire device becomes ineffective to regulate tension at large applied tensions.